1. Field of the Invention
The invention relates to a percussion mechanism used as a breaker, rock-drilling hack, and/or a percussion hammer and, more particularly, relates to a percussion mechanism having a variable speed rotor whose speed variation is achieved corresponding to a pre-selected algorithm.
2. Discussion of the Related Art
Percussion mechanisms of this type are used for instance in electrically powered pavement breakers, rock-drilling jacks, and/or percussion hammers. The percussion mechanisms typically incorporate a motor that rotates in one direction at an essentially constant speed and, via a crank or wobble drive, moves a drive piston (Piston) back and forth, which later on its part, by way of a spring such as a pneumatic spring, operates a percussion piston (Hammer).
In percussion mechanisms driven by a rotary motor, the fixed geometry of the crank gear (crank radius) or of the wobble drive (oscillating stroke) locks in the throw setting of the drive piston. In most cases, the frequency of rotation during a percussion cycle is largely constant due to mass inertia. The stroke length and rotational frequency predetermine an invariable percussion intensity. Therefore, the frequency and intensity of the percussive impact cannot be independently selected.
EP 1 172 180 A2 describes a percussion mechanism driven by a rotary electric motor. The stroke travel setting of the drive piston can be varied either manually or by electric motor. That adjustment mechanism, however, is costly. Moreover, the adjustment mechanism cannot respond to varying kickback conditions within a percussion cycle.
DE 10 2005 030 340 B3 and WO 03/066286 A1 on their part describe percussion mechanisms in which the drive piston is directly actuated by an electric linear motor. The linear motor makes it possible, within certain physical limits, to individually vary the pattern of every percussion cycle. A drawback, however, consists in the fact that the armature and stator are not fully lined up over their respective length and at all times, since they pass each other in linear fashion. It follows that the structural complexity and thus the cost, as well as the weight of the motor, are greater than in the case of a rotary motor whose entire active electromagnetic surface is functionally engaged at all times.